The present invention relates to a power seat for vehicles, and particularly, to a power seat for vehicles including a power-assisted sliding rail structure for carrying a seat mounted thereon.
A power seat with such a sliding rail structure has been disclosed in Japanese Patent Application Laid-Open Publication No. 5-024466.
In this conventional power seat, when the vehicle is subjected to a collision, acceleration or deceleration, a load is applied to a pair of upper and lower sliding rails via a seat member in a sliding direction of the rails. Essentially, this load is transmitted from the upper rail, which carries the seat member, via a gearbox and a lead screw in a drive unit, which is fixed to a front end of the upper rail, and further through a nut member screwed on the lead screw, ultimately to the lower rail.
Considering the case of a front-end collision in which a collision load of several times the weight of an occupant is applied to the upper rail in a forward direction of the vehicle, there develops a significant bending moment in a front end region of the upper rail to which the gear box is fixed. In the, case of a rear-end collision in which a load is applied in a rearward direction of the vehicle, a similar moment develops in a reverse direction.
Reinforcement is required to counter the effect of such a moment. For example, to prevent deformation of the upper rail by the moment, it is necessary to provide reinforcement by making the thickness of the upper rail larger, and to prevent deformation of the lead screw, it is necessary to make the diameter of the lead screw larger. These measures are accompanied by additional cost and weight.
As the collision load is applied directly to the gear box, it is necessary for the gear box to be made of such a material and to have such a construction that can withstand this load. This leads to an extra cost, and a failure to achieve a compact gear box design for efficient use of space and reduction in weight.